The popular use of magnetically recorded information in credit card or other security card applications has created the need for a more secure magnetic medium on which to record or read the information being stored on such a medium. The magnetic material used on credit cards or the like is commonly a low coercivity medium, meaning that a low magnetic field strength of between 300 Oe (Oersted) and 1000 Oe is required to change the pole orientation of the magnetic particles in the medium. The magnetic field strength of a common household magnet is great enough to erase portions of the recorded information on such a medium. To reduce the risk of losing data from magnetic records, magnetic materials have been developed with a higher coercivity range of 2700-4000 Oe which offers complete protection from damage to the magnetic record resulting from magnetic fields commonly encountered in day-to-day activities.
With the development of high coercivity magnetic record material, a corresponding need has developed for magnetic heads with sufficient sensitivity to read and write the new high coercivity material quickly and without undue interference, particularly in applications having multiple tracks in close proximity to each other.
Generally, a magnetic head comprises a coil, a magnetic core and a non-magnetic gap arranged in such a way so that an electric current in the coil will cause magnetic flux to circulate through the core and across the non-magnetic gap.
The core is made of a material having a low magnetic resistance so that the magnetic flux flows within the cross-sectional area of the core. The non-magnetic gap, however, has a high magnetic resistance so that the magnetic flux flows through a similar cross-sectional area that is larger than that of the core.
The flux lines that arc out through the magnetic medium at the non-magnetic gap are used for recording. The flux lines that arc out toward adjacent cores, when multiple track heads are used, will magnetically influence the flux flowing in those adjacent cores.
A magnetic shield is commonly disposed between cores in a multi-track head to reduce cross-talk between the adjacent cores. However, if the shield is placed too close to the core, it results in magnetic flux coupling between the adjacent cores through the shield with a corresponding increase in cross talk. The shield also provides an alternate path for magnetic flux so that instead of circulating across the non-magnetic gap, the magnetic flux flows through the shield resulting in diminished head performance.
One shortcoming of read/write heads for high coercivity media is that such heads generally require a ten-fold increase in magnetic flux circulating in the core. In multiple-track use, the higher magnetic flux level results in excessive cross-talk during a write process when trying to write two adjacent tracks at the same time.
Another shortcoming of known read/write heads for high coercivity media is that the higher write current results in an even greater increase in power dissipation and heat generation in the head. Accordingly, heat sink requirements and low duty cycle requirements may not allow the write head to operate at high throughput speeds which are required in automatic card processing systems, for example, throughput speeds of 700 cards per hour or more.
Yet another shortcoming of some known read/write heads for high coercivity media is that the read/write heads cannot be used with low coercivity media as the materials used to construct the cores have a sufficiently high magnetic remanance such that it would erase the previous encoding on a low coercivity magnetic stripe of 300 Oe, such as that used on a typical credit card, during a read cycle.
Additionally, known materials for high coercivity heads are also mechanically quite soft, in the range of R.sub.B 70, and so the heads tend to wear down quickly and become unuseable. These materials can be coated with a harder material, but then optimum head performance is sacrificed, particularly in read accuracy and encoding characteristics.
Furthermore, head parameters such as inductance, which are understood by the industry and relied upon to measure the quality of head performance, do not accurately describe true head performance. Particularly, it is inaccurate to use inductance to measure the rate of increase of magnetic fields in the write process so as to measure the quality of head performance. It has been found that an indicator such as magnetic rise time, which reflects the speed of generating magnetic fields in response to electrical currents, is a more accurate measure of the performance of a read/write head.
The present invention solves these and other problems associated with existing high coercivity read/write heads.